1. Field of the Invention
The present invention relates generally to electromagnetic relays, more particularly, to a miniature power switching relay specifically designed for mounting on printed circuit boards.
2. Description of the Prior Art
Electromagnetic switching devices, commonly referred to as relays, have been used for many years and there is a continuing need for such a device which is small in size. Yet, moreover, capable of reliably handling relatively high current switching jobs. This requirement for miniaturization together with reliability has become particularly important in recent years because of the increasingly common practice of mounting relays on printed circuit boards.
In the design of an electromagnetic relay and other such electromagnetic devices an important consideration is the design of the "magnetic circuit." The design of an effective magnetic circuit determines to a great extent the current switching capability of the relay and the power needed to operate it. The magnetic circuit of a relay generally includes the core of the relay coil, the relay frame, the armature that moves directly or indirectly through an actuator, and the relay contacts. In addition, the air gaps exist where the core of the relay coil and the armature interface with the relay frame and most importantly between the armature and the core of the coil at an exposed end.
In relay operation electrical current is sent throughout the relay coil. The current running throughout the relay coil sets up a magnetic field in this magnetic circuit and it is the strength of the magnetic field generated in the air gap between the armature and the core of the relay coil at an exposed end that is the force that causes the armature to move into contact with the core of the relay coil at an exposed end therefore, providing the motion to operate the switching of the relay contacts. In the relay, the core of the relay coil, the frame and armature are made of materials that can be easily magnetized. The air gaps, however, resist the establishment of a magnetic field, and the air gap between the armature and the core of the coil has by far the most significant resistance to a magnetic field in the magnetic circuit. In obtaining switching capability for the relay, it is desirable to design effective contact travel distances and rapid movement of the contacts by the armature. It is also desirable to provide the strongest possible magnetic field at this armature gap for the available coil current. This provides for positive and rapid contact movement thus permitting the use of a strong return spring. A strong return spring allows for return movement of the armature when the relay current is removed causing positive and rapid contact movement.
Therefore, the mechanical arrangement of the magnetic coil core, relay armature, resulting air gap and the design of their interfaces significantly affect the ability of the relay to perform its function as an electrical switching device. It is desirable to maintain a minimum air gap between the core and armature. This air gap must be tailored to the design of the relays function achieving the intended movement needed to move the movable contact or contacts the required distance for proper contact switching.
The present invention fulfills the need for a device which is small in size, yet capable of reliably handling high current switching jobs relative to known designs. The present invention solves the high current problem in a small size by using a combination contact assembly. This contact assembly contains a blade and a terminal.
It is known that bi-metal contact assemblies are used in electromagnetic relays. These known electromagnetic relays use bronze and brass materials for the blade and terminal. In addition, the blade and terminal are spot welded together.
A problem with the known brass and bronze materials is that these materials have low current conductivity properties. In addition, spot welding produces a limited contact area for the electrical current to flow through between the blade and the terminal resulting in lower current handling potential.
Accordingly, there is a need for an electromagnetic relay that is small in size yet capable of handling high current switching.
Accordingly there is also a need for an electromagnetic relay with a contact assembly comprised of more conductive material than brass and bronze and having a greater contact surface between the blade and the terminal.
The present invention solves both of these problems. First, the blade and terminal are made of high current conductive materials namely copper alloy and oxygen free copper. Secondly, the parts are ultrasonically welded together which produces a large contact area between the blade and the terminal resulting in higher current handling potential. Therefore, by using materials with high conductivity properties and increasing the contact area between the terminal and the blade the present invention can handle higher currents while maintaining a relatively small overall package size.
As will be described in greater detail hereinafter, the present invention solves the aforementioned and employs a number of novel features that render it highly advantageous over the prior art.